Fluorescence of ZnO Ultrafine Particles Quenched by Naphthothiacarbocyanine Dye in Ethanol: The Effect of Water
✍ Scribed by Sihai Chen; Ulrich Nickel; Xinmin Ren
- Publisher
- Elsevier Science
- Year
- 1995
- Tongue
- English
- Weight
- 131 KB
- Volume
- 176
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
in ethanol by Koch et al. in 1985 (12), the photophysical The interaction between ZnO ultrafine particles and naphthothiand photochemical properties of colloidal ZnO have been acarbocyanine (NTC) dye in ethanol was investigated by monitorintensively studied (13)(14)(16)(17)(18). Two fluorescence bands are ing the variations in intensity of visible fluorescence of ZnO with normally observed for ZnO. One is the excitonic fluoresincreasing concentration of NTC at different temperatures. It was cence, which is caused by the direct combination of phofound that the presence of small amounts of water in the solution toexited electrons and holes. The other is the visible fluoresgreatly affects the aggregation state of NTC and thus the fluorescence, which is the radiation that results from the relaxation cent behavior of ZnO. In the absence of water, a dynamic quenchof the excited electrons on the sites of trapped holes on the ing was observed by NTC dye when its concentration was less surface. The trapping of the photoinduced electron on the than 7 mM and 13 mM at 20ЊC and 42ЊC, respectively. But at higher concentrations, the severe aggregation of NTC resulted in surface of particle has also been found to be very fast and a great decrease of NTC dye concentration in solution, leading to the average diffusion time from bulk to surface has been a decreased quenching ability of NTC. When the quencher was reported to be less than 0.2 ps for a particle of 4 nm diameter dissolved in 95% ethanol (in the mixed ZnO-NTC solution, final (11). This implies that the visible fluorescence of ultrafine water content 0-0.5%), aggregation of NTC did not occur. Howparticles is a reflection of the properties of the particle surever, if the quencher was dissolved in water (final water content face. Therefore, it is possible to investigate the interfacial in mixed ZnO-NTC solution 1.5%-7%), due to the adsorption interaction by utilizing visible fluorescence measurement. of water by ZnO, coagulation of ZnO particles occurred first, then Cyanine dyes, which are widely used as spectral sensitiza new aggregation state of NTC-containing water was formed on ers in photography (19), show some interesting behaviors the ZnO surface, leading to a stronger fluorescence quenching.